The present invention relates to a magnetic tape cartridge, and more particularly to a magnetic tape cartridge of the type employing a single reel having a magnetic tape wound thereon, and wherein a leader tape at the end of the wound tape is used to draw the magnetic tape from a tape-drawing opening formed in the housing of the tape cartridge by a tape-drawing device of a recording/reproducing unit, thereby causing the tape to run along a tape travel path in the recording/reproducing unit so as to allow information to be read from and written onto the tape.
In a conventional magnetic tape cartridge used as a recording medium for a computer or the like, a magnetic tape is wound on a single reel, and this reel is rotatably housed in a cartridge case composed of an upper cartridge half and a lower cartridge half.
When this magnetic cartridge is in use, the magnetic tape is drawn out from an opening in the cartridge case. When the cartridge is not in use, the magnetic tape is completely wound on the reel, the leader tape (by which the tape is extracted from the cartridge to introduce the magnetic tape into the tape travel path) is retained at an end surface of the cartridge case, the reel is locked against accidental rotational movement by a suitable lock device such as a reel brake, and the tape opening is closed by a lid.
Because important information is stored in such a magnetic tape cartridge, the cartridge must be constructed so as to prevent the magnetic tape from being accidentally drawn out of the cartridge. Cutting and jamming of the tape are further potential problems that must be prevented. Specifically, the reel brake is used to prevent rotation of the reel as described above, and a splicing tape having a high bonding force is used for connecting the magnetic tape and the leader tape in locations where tape cutting is particularly prone to occur.
With respect to dimensional standards for the above splicing tape, industry standards require that the overall thickness be not more than 28.38 .mu.m, the substrate thickness be not more than 23.3 .mu.m, the bonding layer thickness be not more than 5.08 .mu.m, with the length of the splicing tape be in the range of 11,811 mm to 20.32 mm. With respect to the bonding strength of the splicing tape, there is required an adhesive force not less than 190.3 g/12.2 mm, and as to the required holding force, the splicing tape joining the magnetic tape and the leader tape together must withstand a tensile strength of 2.27 kg (5 pounds) for not less than 60 seconds.
Conventionally, bonding of the splicing tape has been carried out in the manner illustrated in FIG. 7. Namely, the splicing tape 22 with an overall length L.sub.0 has substantially equal right and left lengths L.sub.2 and L.sub.1, measured with respect to a tape abutting position C at which a magnetic tape 20 and a leader tape 21 are joined. The length of the splicing tape 22 is, for example, 14 mm or 20 mm. With these values, the above standards are sufficiently satisfied, even if the above bonding method is employed. Generally, the temperature and humidity of a room in which a computer is installed are considerably strictly controlled, and under such conditions it has been thought that the above-described tape cartridge is satisfactory.
However, during long-term use of such a magnetic tape cartridge, the cartridge may not always be used only in a good environment, and the leader tape 21 and the magnetic tape 20, though rarely, sometimes have been separated or cut from each other at the splicing tape 22.
An extensive study has been made in an attempt to uncover the cause of this problem, and as a result it has been found that the problem is attributable to the construction of the tape travel path in the recording/reproducing device. Namely, several guide rollers 60, as shown in FIG. 8, are provided the tape travel path, and when the splicing tape 22 is contact with the guide roller 60, as also shown in FIG. 8, the leader tape 22 sometimes does not curve properly along the outer periphery of the guide roller 60 , but is rendered straight, thus causing it to separate from the splicing tape 22.
The maximum angle .theta. winding around the guide roller reaches 75 degrees. The leader tape 21 is made, for example, of polyethylene terephthalate, and has a thickness of 0.188.+-.0.0188 mm. It has been thought that if the temporary spring-back force of the leader tape 21 (which has a greater rigidity than the magnetic tape 20) against the bonding force meets the above conventional standards, there would be no danger separation and the cartridge would operate satisfactorily; however, nevertheless, peeling has sometimes occurred.
Since the maximum length of the splicing tape 22 is limited by the above standard, it might be thought that this problem could still easily be overcome by the use of a splicing tape having a greater bonding force. However, as a practical matter, there is not currently available on the market a splicing tape having a better bonding ability than those now in use, and to develop a slicing tape having a greater bonding strength requires very much time and expense and would likely incur an increased manufacturing cost. Therefore, in has generally not been possible to solve the above problem by increasing the bonding force of the splicing tape.
Also, it might be considered to use an adhesive to avoid the above-mentioned peeling. However, if an adhesive is used, additional steps are needed, such as cutting of the splicing tape and coating of the adhesive, which not only lowers productivity but also invites additional problems such as squeezing-out of the adhesive along the edges of the tape. This would significantly lower the yield rate.